Corrosion inhibitors



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Unitd raes Free 3,029,127 CORROSION INHIBITORS Ernest L. Pollitzer,Hinsdale, IlL, assiguor, by mesne assignments, to Universal Oil ProductsCompany, Des Plaines, 111., a corporation of Delaware No Drawing. FiledNov. 26, 1957, Ser. No. 698,917 12 Claims. (Cl. 21--2.7)

This invention relates to a novel method of inhibiting corrosion andmore particularly to the use of a substantially water soluble inhibitorto prevent corrosion of metallic surfaces upon contact with water.

Corrosion of metallic surfaces, particularly iron and steel, in contactwith fresh or salt water or various aqueous solutions, results in aserious economical loss. There is an urgent need for, and the presentinvention provides, improved water soluble corrosion inhibitors whichwill retard and/or prevent such corrosion.

While the novel inhibitors of the present invention may be used in anysystem wherein water or aqueous solutions contact metallic surfaces, thefollowing specific examples are set forth as illustrative, but notlimiting, instances in which the inhibitors of the present invention areuseful. Storage tanks, pipe lines and the like containing petroleum oilsor other organic compounds generally contain water which causescorrosion of the metallic surfaces. For example, in storage tanks thewater settles to the bottom and causes corrosion of the internalsurfaces of the storage tank. The water soluble corrosion inhibitor ofthe present invention will dissolve in the water phases and will serveto retard and/ or prevent such corrosion. Another example is in thestamping, rolling or other working of metal in which a water stream issprayed or otherwise used as a coolant. Because these operations areeffected at high temperature, the cooling water often causes extensivecorrosion. Such corrosion is avoided by incorporating the corrosioninhibitor of the present invention in the water spray. Still anotherapplication is in the salt-ice water solutions used as refrigerants, forexample, in railroad cars, trucks, etc. When used in railroad cars, thesalt solution not only effects corrosion of the railroad cars but alsodrips onto the rails and causes corrosion thereof. It is readily seenthat such corrosion is a serious economical problem because it requiresfrequent replacement of rails, which is expensive both in manpower andin material cost. Still other applications include boiler Water, acidsolutions such as pickling solutions, etc.

In one embodiment the present invention relates to a method of retardingcorrosion of a metal upon contact with water which comprises effectingsaid contact in the presence of a corrosion inhibitor comprising amonoalkali metal salt of an alkyl acid orthophosphate, the alkyl groupcontaining from 9 to about 18 carbon atoms.

In a specific embodiment the present invention relates to the method ofretarding corrosion of a metal upon contact with water which compriseseffecting said contact in the presence of the monosodium salt of decylacid orthophosphate.

In another embodiment the present invention relates to water containingas a corrosion inhibitor a mono-alkali metal salt of an alkyl acidorthophosphate, in which the alkyl group contains from 9 to about 18carbon atoms.

It will be noted that the novel corrosion inhibitors of the presentinvention are mono-alkali metal salts of specific alkyl orthophosphates.As will be shown in the examples appended to the present specifications,it is essential that, when using alkyl acid orthophosphate, the alkylgroup contains from 9 to about 13 carbon atoms and preferably from aboutto about 14 carbon atoms. When a dialkyl orthophosphate is employed, atleast one of the alkyl groups must contain from 9 to about 18 carbonatoms and preferably from about 10 to about 14 carbon atoms in order toachieve the improved results.

As will be shown in the following examples, the limitations hereinbeforeset forth are critical in order to obtain the improved results of thepresent invention. :Sur-

prisingly, it has been found that the mono-alkali metal salt of octylacid orthophosphate (alkyl group containing 8 carbon atoms) did notproduce the improved results obtained by corresponding compounds having10 or 13 carbon atoms in the alkyl group. Also it has been found thatthe mono-alkali metal salt appears unique for this purpose because thedi-alkali metal salts did not produce these improved results.

While it is preferred to utilize the mono-alkali metal salt of the monoalkyl acid orthophosphate, further limited in the manner hereindescribed, in another embodiment of the invention the mono-alkali metalsalts of the dialkyl orthophosphates maybe employed, provided at leastone of the alkyl groups contains from 9 to about 18 carbon atoms. Insome cases the dialkyl orthophosphate salts or even the mono alkyl acidorthophosphate salts containing 16 to 18 carbon atoms may not be aswater soluble as the corresponding salts containing a fewer number ofcarbon atoms in the alkyl group or groups as, for example, from about 9to about 16. However, in some cases, the requirement for complete watersolubility is not necessary because the partly soluble or readilydispersible salt will serve the intended purpose to prevent corrosion ofthe metallic surfaces and, accordingly, such salts may be satisfactorilyemployed. Y

From the above discussion, it is seen that the particular alkylorthophosphates used in preparing the salt must be selected withreference to the very strict requirements heretofore set forth. Thesestrict requirements .will be further elaborated upon in the examplesappended to the present specification.

Any suitable alkali metal salt of the alkyl or dialkyl orthophosphatesmay be utilized in the present invention. A preferred alkali metalcomprises sodium and thus a preferred salt comprises a monosodium saltof the specified alkyl acid orthophosphate. Other alkali metals whichmay be used in preparing the salt include potassium, lithium, rubidiumand cesium. Of these, potassium and lithium generally are preferredbecause of their ready avail ability and lower cost.

In most cases it is preferred that the alkyl group of 9 to about 18carbon atoms contains some branching in the chain. This appears toimprove the corrosion inhibiting properties of the salt. As will beshown in the following examples, a monodecyl acid orthophosphate derivedfrom C Oxo alcohols-Le. alcohols containing highly branched alkylchainsgave a monosodium salt which was a very effective corrosioninhibitor.

Illustrative preferred salts for use in the present invention includemonosodium salt of monyl acid orthophosphate, monosodium salt of decylacid orthophosphate, monosodium salt of undecyl acid orthophosphate,monosodium salt of dodecyl acid orthophosphate, monosodium salt oftridecyl acid orthophosphate, monosodium salt of tetradecyl acidorthophosphate, monosodium salt of pentadecyl acid orthophosphate,monosodium salt of hexadecyl acid orthophosphate, monosodium salt ofheptadecyl acid orthophosphate, monosodium salt of octadecyl acidorthophosphate, monosodium salt of mixed monoand didecyl orthophosphate,monosodium salt of mixed monoand diundecyl orthophosphate, monosodiumsalt of mixed monoand didodecyl orthophosphate, monosodium salt of mixedmonoand ditridecyl orthophosphate, monosodium salt of mixed monoandtetradecyl orthophosphate, etc. It is understood that these differentsalts are not necessarily equivalent. The monopotassium salts andmonolithium salts corresponding to the monosodium salts recited abovelikewise are particularly suitable for use in the present invention, butnot necessarily equivalent.

The salts may be prepared in any suitable manner. In many cases thedesired mono alkyl acid orthophosphate or dialkyl orthophosphate isavailable commercially and may be purchased in the open market. When notso available, the specific alkyl acid orthophosphate ay be syntheticallyprepared by reacting the desired alcohol with the desired stoichiometricamount of phosphorus oxychloride or phosphours pentachloride. The mixedmonoand dialkyl acid orthophosphates may be cheaply and convenientlyprepared by reaction of the desired alcohol with phosphorus pentoxide.

The salt is prepared readily by reacting the alkyl acid orthosphosphatewith the alkali metal hydroxide, alkali metal carbonate or othersuitable alkali metal salt, preferably in the presence of a suitablesolvent as, for example, an alcohol such as ethanol, 1 or Z-propanol, abutanol, etc., ethers, aromatic or aliphatic hydrocarbons, etc. Ingeneral, the reaction is effected by mixing equal molar proportions ofthe alkali metal hydroxide and alkyl orthophosphate, and reacting thesame at a temperature of from about 20 to about 80 C. and morepreferably of from about 40 to about 60 C. In some cases highertemperatures may be employed but, in any event, the temperature shouldnot exceed that at which decomposition of the salt occurs. In some casesthe salt precipitates and thus is readily collected and separated fromthe solvent. In other cases the solvent may be separated by heating toevaporate the same. In still another embodiment, the salt may be used asa solution in the sol vent and, in cases where the salt does notprecipitate out of solution, it may be recovered and used in the samesolvent employed in the preparation of the salt.

As hereinbefore set forth, the salts prepared in the above manner'areutilized as water soluble or substantially water soluble corrosioninhibitors. The salt is incorporated in water, aqueous solutions orsubstrates containing water or contacting water, in a sufficientconcentration to effectively retard corrosion of metallic surfaces.Generally the salt is used in a concentration of below about 1% byweight of the water, aqueous solution or substrate containing water, andusually in a concentration within the range of from about 0.001% toabout 1% and more particularly from about 0.01% to about 0.5% by weightthereof, although higher concentrations may be employed when excessivecorrosion is encountered. It is understood that the corrosion inhibitormay be used in conjunction with other additives which are incorporatedin the substrate for various reasons.

The following examples are introduced to illustrate further the noveltyand utility of the present invention but not With the intention ofunduly limiting the same.

Example I The corrosion inhibior of this example is the monosodium saltof decyl acid orthophosphate and was prepared by reacting equal molarproportions of sodium hydroxide with decyl acid orthophosphate purchasedin the open market and prepared from Oxo alcohols. The salt was preparedby mixing sodium hydroxide with the decyl acid orthophosphate at roomtemperature, utilizing Z-propanol as the solvent. The salt was recoveredby evaporating the solvent under vacuum.

The salt prepared in the above manner was evaluated as a corrosioninhibitor by the following method. A 600 cc. beaker was used as thereaction vessel and 300 cc. of a 5% sodium chloride solution containingthe inhibitor was introduced into the beaker. A 0.5" x 3 x A mild steelstrip was inserted in the beaker and held in a horizontal position withone end resting on a glass rod. The sodium chloride solution was stirredby a single blade stirrer revolving at 250 rpm. Air was continuouslybubbled in at the rate of 5.6 liters per hour.

When evaluated in the above manner, a steel strip, after six hoursexposure in a brine not containing in hibitor, showed a weight loss of22-24 mg.

0.05% of the salt prepared in the above manner was. incorporated inanother sample of the brine and, when evaluated in the above manner, theloss of weight was only 2.6 mg. after six hours exposure. It will benoted that this inhibitor considerably retarded corrosion of the steelstrip.

Example II In a run similar to that described in Example I themonosodium salt of decyl acid orthophosphate was incorporated in anothersample of the brine in a concentration of 0.03% by weight and, whenevaluated in the manner described in Example I, the loss of weight wasonly 2.9 mg. Here again it will be noted that the corrosion inhibitorwas effective in retarding corrosion of the steel strip.

Example III The corrosion inhibitor of this example is the monosodiumsalt of tridecyl acid orthophosphate and, when evaluated in anothersample of the brine and in the manner described in Example I, utilizing0.05% by weight of the inhibitor, the loss in weight was only 2.1 mg. Inanother run, using 0.03% by weight of this inhibitor, the loss in weightalso was only 2.1 mg. Thus it will be noted that this inhibitor isequally effective even at the low concentration of 0.03% by weight.

Example IV The corrosion inhibitor of this example was the monosodiumsalt of mixed monoand ditridecyl orthophosphate, the latter beingcommercially available and purchased on the open market. This inhibitorwas evaluated in another sample of the brine and substantially in thesame manner as described in Example III, utilizing 0.05% by weight ofthe inhibitor. After six hours exposure the loss in weight was 3.2 mg.It will be seen that the mixed monoand ditridecyl orthophosphate salt isan effective inhibitor but is not as good as the corresponding salt ofthe monotridecyl alkyl acid orthophosphate. However, the mixed monoandditridecyl orthophosphates may be purchased at a lower price than themonotridecyl acid orthophosphate and, therefore, the slightly poorerresults may be justified economically by the lower cost.

Example V As hereinbefore set forth, it is essential that the alkylgroup of the alkyl acid orthophosphate contains at least 9 carbon atoms.In an evaluation of the monosodium salt prepared from octyl acidorthophosphate (containing 8 carbon atoms in the alkyl group) in anothersample of the brine and in the same manner as described in Example I,utilizing 0.05% by weight of inhibitor, the loss in weight was 10.0 mg.after six hours exposure. It will be noted that this is from 4 to 5times greater than the reduction in weight obtained by the saltsprepared from decyl (containing 10 carbon atoms in the alkyl group) andtridecyl (containing 13 carbon atoms in the alkyl group)orthophosphates.

Example VI As hereinbefore set forth, the mono-alkali metal salt must heused for the improved results. This is illustrated in the presentexample in which the disodium salt of the mixed monoand ditridecylorthophosphate was evaluated in another sample of the brine and in thesame manner as described in Example I, utilizing 0.05 by weight ofadditive. The loss in weight after six hours exposure was 14.3 mg. byweight. This is to be compared with the results reported in Example IV(3.2 mg. weight loss) using the monosodium salt of the mixed monoandditridecyl orthophosphate.

Example VII The disodium salt of octyl acid orthophosphate also wasevaluated in the same manner described in Example I in another sample ofthe brine. The loss in weight, when using 0.05% by Weight of the saltwas 13.7 mg. It will be noted that the disodium salt of the octyl acidorthophosphate Was even of lower potency than the monosodium salt of thesame orthophosphate.

Example VIII As also hereinbefore set forth, when the dialkylorthophosphate is utilized in preparing the salt, it is essential thatat least one of the allzyl groups contains from 9 to about 18 carbonatoms. This is illustrated in the present example in which 0.02% byweight of the monopotassium salt of mixed amyl octyl orthophosphate wasevaluated in the same manner heretofore described. The loss in weightwas 9.8 mg, which is considerably higher {4 to 5 times) than obtainedwith the corrosion inhibitors of the present invention.

I claim as my invention:

1. The method of retarding corrosion of a ferrous metal upon contactwith water which comprises effecting said contact in the presence of aWater-soluble corrosion inhibitor consisting essentially of amono-alkali metal salt of an alkyl orthophosphate, wherein the alkylgroup contains from 9 to about 18 carbon atoms.

2. The method, of retarding corrosion of a ferrous metal upon contactwith water which comprises effecting said contact in the presence of awater-soluble corrosion inhibitor. consisting essentially of themonosodium salt of decyl acid orthophosphate.

3. The method of retarding corrosion of a ferrous metal upon contactwith water which comprises effecting said contact in the presence of awater-soluble corrosion inhibitor consisting essentially of themonosodium salt of undecyl acid orthophosphate.

4. The method of retarding corrosion of a ferrous metal upon contactwith water Which'comprises elfecting said contact in the presence of awater-soluble corrosion inhibitor consisting essentially of themonosodium salt of dodecyl acid orthophosphate.

5. The method of retarding corrosion of a ferrous metal upon contactwith water which comprises effecting said contact in the presence of aWater-soluble corrosion inhibitor consisting essentially of themonosodium salt of tridecyl acid orthophosphate.

6. Water containing a water-soluble corrosion inhibitor consistingessentially of a mono-alkali metal salt of an alkyl orthophosphatewherein the alkyl group contains from 9 to 18 carbon atoms.

7. Water containing a water-soluble corrosion inhibitor consistingessentially of the monosodium salt of decyl acid orthophosphate. v

8. Water containing a Water-soluble corrosion inhibitor consistingessentially of the monosodiurn salt of undecyl acid orthophosphate.

9. Water containing a water-soluble corrosion inhibitor consistingessentially of the monosodium salt of dodecyl acid orthophosphate.

10. Water containing a water-soluble corrosion inhibitor consistingessentially of the rnonosodium salt of tridecyl acid orthophosphate.

11. Water containing a Water-soluble corrosion inhibitor consistingessentially of a mono-alkali metal salt of a mixed monoand dialkylo-rthophosphate, wherein the alkyl group of said mono alkylorthophosphate and at least one of the alkyl groups of the dialkylorthophosphate contains from 9 to about 18 carbon atoms.

12. Water containing a water-soluble corrosion inhibitor consistingessentially of the monosodium salt of a mixed monoand ditridecylorthophosphate.

References Qited in the file of this patent UNITED STATES PATENTS HughesJune 23, 1959

1. THE METHOD OF RETARDING CORROSION OF A FERROUS METAL UPON CONTACTWITH WATER WHICH COMPRISES EFFECTING SAID CONTACT IN THE PRESENCE OF AWATER-SOLUBLE CORROSION INHIBITOR CONSISTING ESSENTIALLY OF A MONO-ALKLIMETAL SALT OF AN ALKYL ORTHOPHOSPHATE, WHEREIN THE ALKYL GROUP CONTAINSFROM 9 TO ABOUT 18 CARBON ATOMS.